Multifrequency dual ridge waveguide slot antenna



y 6, 1965 J. H. PROVENCHER 3,193,830

MULTIFREQUENCY DUAL RIDGE WAVEGUIDE SLOT ANTENNA Filed July 25, 1963 2Sheets-Sheet 1 FIG. I

( PRIOR ART) FIG. 2

(PR/OI? ART) /0 IN VENTOR. JOSEPH H. PROVE/VCHE'I? 67M 4. (AL

y 5, 1955 J. H. PROVENCHER 3,193,830

MULTIFREQUENCY DUAL RIDGE WAVEGUIDE SLOT ANTENNA Filed July 25, 1963 2Sheets-Sheet 2 E 25 0 2 0.250 X 0.500 L000" H H l '5 2o Z |-0.250" 3 l 23 sro. WAVEGUIDE m 0.2s0x 0.050 0250x0700 9 0.250 x0750 w I5 E 3 SINGLERIDGE 0 0.567 I 0.800

WI 2 WAVEGUIDE I0 I I I 2100 2900 aloo 3300 3500 FR EQUENCY IN Mc/s INVENTOR.

F, 6 JOSEPH h. PROVENCHER United States Patent 3,193,830 MULTIFREQUENGYDUAL RIDGE WAVE- GUlDE SLOT ANTENNA Joseph H. Provencher, San Diego,Calif., assignor to the United States of America as represented by theSecretary of the Navy Filed July 25, 1963, Ser. No. 297,727

6 (Ilaims. (Cl. 343-771) (Granted under Title 35, US. Code (1952), sec.266) The invention described herein may be manufactured and used by orfor the Goverrunent of the United States of America for governmentalpurposes without the payment of any royalties thereon or therefor.

The present invention relates to an improved antenna and moreparticularly, to an improved ridged waveguide antenna and specifically,to a dual ridge waveguide antenna.

The present invention represents an extension of the principles setforth in co-pending application Serial No. 167,983, filed January 22,1962, titled Ridged Waveguide Antenna. In the aforementioned co-pendingapplication the requirements of radiation and receiving ofelectromagnetic energy are set forth as well as prior art techniques andshortcomings.

Briefly however, a necessary requirement for the design of multi-elementslotted arrays for low-side lobe application is an element spacing ofapproximately one half free space wave length. Because of the physicalsize of standard waveguides however, this requirement cannot be met. Inorder to obviate this shortcoming a ridge, or metal strip is insertedinto the waveguide and fastened to one wall as set forth in FIG. 1 andby so doing the range of required frequencies can be extended to lowerfrequencies. The wave lengths of the frequencies propagated can becontrolled to some degree by a proper choice of the ridge parameters aand b in FIG. 1. This technique has been used for planar arrays and isquite Well known. The waveguide is then slotted in variousconfigurations to give a desired radiation pattern. Individual elementsi.e. individual arrays are then assembled in an array of arrays as shownin FIG. 2.

In many instances in antenna design, the use of the same area occupiedby an antenna for more than one function is desirable. This may beespecially so on small ships where space may be at a premium. Severalschemes are in present use which utilize the same aperture area for bothradar and identification function. For the slotted array case even withthe use of the ridge and the adjacent slot as set forth in theaforementioned co-pending application, the possibility of using theaperture for other functions is minimized due again to the one-half freespace wave length spacing required for low-side lobes and the preventionof a multiplicity of beams.

An object of the present invention is to provide an improved ridgedwaveguide antenna.

A further object of the present invention is to provide an improvedridged waveguide antenna wherein two or more functions may be carriedout in the same antenna aperture.

A further object of the present invention is to provide an antenna arraywhich has the advantages of an adjacent slotted ridged waveguide antennaand in addition is ca- 3,1933% Patented July 6, 1965 FIG. 2 is anillustration of a prior art array of arrays of FIG. 1;

FIG. 3 illustrates one embodiment of the present invention showing theplacement of two ridges in a standard waveguide on the same wall;

FIG. 4 illustrates an embodiment of the present invention showing theplacement of the slot in. the wall of the ridged waveguide;

FIG. 5 illustrates another embodiment of the invention; and

FIG. 6 is a graph of Waveguide characteristics.

In the prior art ridged waveguide antennas a conventional rectangularwaveguide 10 having walls 11, 12, 13]

and 14 is utilized. A loading ridge is placedon one wall, such as 12,and has walls 15, 16 and 17 defining the ridge area. The dimension b ofwalls 15 and 17 of the loading ridge define the extent to which theridge extends into the interior of the waveguide lil and a dimension awhich is symmetrical about the center line or" the waveguide 10 definesthe length of wall 16.

An array of arrays, such as those set forth in FIG. 1, would be utilizedas set forth in FIG. 2 wherein individual arrays It) have a loadingridge on one wall and slots cut in the wall opposite the wall upon whichthe loading ridge is mounted. Thus, with respect to one of the arrays 10slots 18 are cut in wall 11 which is opposite wall 12 upon which theloading ridge is mounted.

In the co-pending application Serial No. 167,983, filed January 22,1962, titled Ridged Waveguide Antenna of Joseph H. Provencher radiatingslots are cut in the same wall that the loading ridge is mounted on. Inthe addition radiating slots are also cut in the wall upon which theloading ridge was mounted and within the area defined by the loadingridge. By doing this it was found that two different frequencies ofpropagation could be utilized within the same aperture. However, theside lobe pattern is not ideal nor are a multiplicityof beams prevented.

In the present invention as shown in FIG. 3, a section of rectangularWaveguide such as 20 having opposite walls 21, 22, and opposite walls23, 24 is utilized and two loading ridges as at 25, 2e are mounted onone of the walls as on wall 24. In FIG. 3 the loading ridges 24 and 25are illustrated as being symmetrical about the longitudinal center axisof the waveguide element 20.

FIG. 4 illustrates an individual array and the placement of slots in thearray within the areas bounded by the loading ridges. Again a section 20of rectangular waveguide is utilized having opposite walls 21, 22 andopposite walls 23, 24. Loading ridges 25 and 26 are again attached towall 24. Slots 27 are cut in the wall 24 of the waveguide element 20within the area bounded by the loading ridges 25 and 26 and extend alongthe longitudinal axis of the waveguide 20. These are cut slightlygreater in length than one half the free space wave length at thefrequency of propagation and are spaced longitudinally one half the freespace wave length.

In addition, radiating slots 28 are cut in the wall 24 within the areabounded by loading ridge :25 and slots 29 are cut in wall 24 within thearea bounded by loading ridge 26. In this embodiment using dual ridgesthe requirement for approximately one half wavelength spacing is metwhile side lobes are suppressed and a multiplicity of beams prevented.

The embodiment of FIG. 5 illustrates an array which is capable ofperforming three functions within the same aperture. In this instance arectangular waveguide element 30 is used. The waveguide has oppositewalls 31, 32 and opposite walls 33, 34. Mounted on one wall 34 areloading ridges 35 and 36. Mounted within loading ridge 35 is anotherloading ridge 37 while mounted within loading ridge 36 is anotherloading ridge 33. Mounted on the center line of waveguide element 3d isanother loading ridge 39 approximately the same dimension as 37, 38.Slots at are cut in the Wall 34 extending longitudinally of the axis ofthe Waveguide 30 and outside the area bounded by loading ridges 35, 3d.Slots it are cut in the wall 34 outside the area bounded by loadingridge 3% and Within the area bounded by loading ridge 36. In addition,the face of the Wall 34 has slots cut in it within the area bounded byloading ridge T e same applies to loading ridge 35. Within the areabounded by it and in the face of Wall 34 and outside the area bounded byloading ridge 37 are slots 43. In addition, slots 44 are cut in the faceof Wall 34 within the area bounded by loading ridge 3'7. Slots 45 arecut in face of Wall 34 within the area bounded by loading ridge 39.

By utilizing such a configuration, i.e., through the use of loadingridges Within loading ridges a multiplicity of frequencies may beattained, for example, as regards a radar system. The extension of thedual ridge technique to the radar array is a logical sequence since ahigh gain requirement is usually desired, and this may be achieved byplacing individual arrays or elements in a side-by-side manner in alarge array. The typical example might require the long range searchradar, the height finding radar, and identification function to operatesimultaneously on a small ship. The three antennas for these threeindependent operations could all occupy the same aperture area in anarray comprising individual elements such as those set forth in FTG. 5.The three waveguides required could be cascaded into one large flatplanar array.

It is to be noted however, that the invention is limited by the physicalsizes of the waveguides used, and these are necessarily dictated bydesired operating frequencies. By judicious choice of the spacing,proper ridge parameters and the operating frequencies, a dual ridgearray capable of any in ependent operation in three frequency bands canbe realized. The concept could also be extended to a circular array orto other configurations by proper choice of spacing in elements.

Spacing of the slots is approximately one half guide wavelength and thelength of the slots is approximately one half guide wavelength as setforth in the aforementioned co-pending application.

In the operation of the embodiments of the present invention theantennas may be center-fed or end-fed, short circuited or loaded at theend. In addition, through the use of a slot longer than one halfWavelength at the operating frequency, the bandwidth restrictions of theresonant slot are avoided. The shorting plate at the end of theWaveguides and the manner in which the elements are fed is notillustrated in that they form no part of the present invention.

With the configuration of the present invention the interior areasbounded by the ridges may be used as additional Waveguides at higherfrequencies and, additionally, these waveguides may in turn be fittedwith ridges so that the scheme may be utilized as a cascaded system,being limited only by the physical sizes of the Waveguides 2 used. Thisallows the use of a numbe of frequency bands in the same aperture areaeach independently fed, and capable of operation simultaneously.Experimental data, which is set forth in FIG. 6, taken with a dual ridgewaveguide demonstrates that the propagation characteristics of standardwaveguides and single ridge waveguides can be duplicated in the dualridge Waveguides. The comparison of these waveguides characteristics andconfigurations in regard to the guide wavelengths are given in FIG. 6.The combinations of these two facts allow the cons ruction of multipleband arrays in the same aperture. Obviously many modifications andvariations of the present invention are possible in the light of theabove teachings. It is therefore to be understood that Within the scopeof the appended claims the invention may be practiced otherwise than asspecifically described.

What is claimed is: 1. An antenna comprising: a rectangular Waveguide; amultiplicity of loading ridges mounted on and extending internally ofthe waveguide; radiating slots located adjacent to the loading ridges inthe same wall that the loading ridges are mounted on for radiatingenergy at a first frequency; and other radiating slots located in thesame wall that the loading ridges are mounted on and within the areasbounded by said loading ridges for radiating energy at anotherfrequency. 2. An antenna as set forth in claim 1 wherein: said radiatingslots located adjacent to said ridges and said other slots locatedwithin the areas bounded by said ridges are parallel to the axis ofpropagation of energy in said waveguide. 3. An antenna as set forth inclaim 1 wherein: the dimensions of certain of the loading ridges differso that the wave length of frequencies propagated from the ridgesdiffer. 4. An antenna as set forth in claim 1 wherein: said multiplicityof loading ridges comprises at least a first and second group; saidfirst group having different physical dimensions than the second group;and one of said first and second groups being mounted within the otherof said first and second groups. 5. An antenna as set forth in claim 1wherein: said multiplicity of loading ridges are mounted on the samewall of the waveguide. 6. An antenna as set forth in claim 4 wherein:said other radiating slots are located Within the areas defined by saidat least first and second groups; the radiating slots associated withsaid first group lying outside the areas defined by said second group;and the radiating slots associated with the second group lying outsidethe areas defined by said first group.

References Cited by the Examiner UNITED STATES PATENTS 2,807,018 9/57Woodward 343-770 HERMAN KARL SAALBACH, Primary Examiner.

1. AN ANTENNA COMPRISING: A RECTANGULAR WAVEGUIDE; A MULTIPLICITY OFLOADING RIDGES MOUNTED ON AND EXTENDING INTERNALLY OF THE WAVEGUIDE;RADIATING SLOTS LOCATED ADJACENT TO THE LOADING RIDGES IN THE SAME WALLTHAT THE LOADING RIDGES ARE MOUNTED ON FOR RADIATING ENERGY AT A FIRSTFREQUENCY; AND OTHER RADIATING SLOTS LOCATED IN THE SAME WALL THAT THELOADING RIDGES ARE MOUNTED ON THE WITHIN THE AREAS BOUNDED BY SAIDLOADING RIDGES FOR RADIATING ENERGY AT ANOTHER FREQUENCY.